Background on Medium Vessel Occlusion
Acute ischemic stroke (AIS), i.e. brain ischemia due to a blocked brain artery, are fatal and debilitating. They comprise 85% of all strokes, and almost invariably lead to severe disability or even death, if left untreated. Until few years ago, intravenous tissue plasminogen activator (tPA) treatment was the only available treatment, but due to the narrow therapeutic window and numerous contraindications, less than 10% of AIS patients on a population basis receive this treatment, and its effectiveness is limited.
In 2015 however, as a consequence of ESCAPE (and other) trial that was led by us and was a pan-Canadian effort, endovascular stroke treatment (EVT), i.e. mechanical clot removal, has been proven to be safe and effective in AIS due to large vessel occlusion, i.e. occlusion of the terminal internal carotid artery and M1 segment of the middle cerebral artery. Compared to intravenous alteplase, EVT is much more effective in opening the occluded vessel segment, and this has substantially improved the prognosis of acute ischemic stroke patients – the number needed to treat for EVT compared to best medical care including intravenous alteplase with regard to a good functional outcome is 2.6 – one of the lowest throughout modern medicine .
However, all the previous randomized EVT trials that have exclusively included patients with LVOs. Patients with medium vessel occlusions (MeVOs), i.e. M2, M3, A2, A3, P2 and P3 occlusions, who make up a large percentage of AIS patients - M2 is the second most common occlusion site in AIS – were not included at all 2. Thus, there is currently no high-level evidence to suggest safety and efficacy of EVT in MeVO strokes. This is also reflected in current North American and European stroke treatment guidelines, which do not contain a clear endovascular treatment recommendation for MeVO strokes due the lack of randomized data.